High-intensity radiation source comprising rotating arc



p 1968 H. c. LUDWlG 3,378,713

HIGH-INTENSITY RADIATION SOURCE COMPRISING ROTATING ARC Fileci June 5, 1965 2 Sheets-Sheet 1 INVENTOR.

WITNESSES N d J M BY Howard C Lu w|g H. c. LUDWlG 3,378,713

HIGH-INTENSITY RADIATION SOURCE COMPRISING ROTATING ABC 2 Sheets-Sheet Z April 16, 1968 United States Patent 3,378,713 HIGH-INTENSITY RADIATION SOURCE COMPRISING ROTATING ARC Howard C. Ludwig, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., :1 corporation of Pennsylvania Filed June 8, 1965, Ser. No. 462,359 7 Claims. (Cl. 313--32) ABSTRACT OF THE DISCLOSURE An arc-discharge apparatus particularly adapted as a high intensity light source with an improved electrode structure. The arc-discharge is constricted as a small cross-sectional plasma and a portion of the plasma is circulated through an aperture extending through the anode. The hollow elongated anode has an internal core portion with a conductor spirally wound thereabout, in order to provide an exterior magnetic field transverse to the are path. The resulting force causes the arc to be displaced in a rotational direction on the anode end surface allowing for improved heat dissipation.

This invention relates to high-intensity, arc-discharge light sources and, more particularly, to an improved anode construction to enable such sources to be operated at higher power inputs and greater efiiciencies.

It is desirable in such present high intensity light sources to operate the light-producing arc in a high ambient pressure and to also use a high input power. Such high intensity light sources are generally described in copending application Ser. No. 261,756, filed Feb. 28, 1963, and assigned to the present assignee now Patent No. 3,280,360, dated Nov. 18, 1966.

The use of a high gas pressure in such devices causes the arc discharge to become constricted and this, in conjunction with the high input power, increases greatly the current density in the arc plasma column as well as at the anode electrode surface. This high current density are at the anode surface imposes a difiicult heat transfer problem in removing the heat thereby generated through the wall of the water-cooled anode. As a result, the inability to effectively remove this generated heat limits the amount of electrical power that may be used in the arc-discharge apparatus.

To overcome this problem, it is known in various arts to provide a magnetic coil to produce a magnetic field about the are and thereby create a component of force which will rotate the are around a circular path. In this way, a sustained anode spot in any one particular position on the anode is avoided and the problem of heat generated is lessened.

Such prior magnetic coils, however, have been found unsuitable for the present light source as they have been applied external to the anode and have been cumbersome and bulky in their configuration. The geometric configuration of the arc-discharge light source used with the present invention requires that the anode be free from large devices external of it as such devices create a shadow in the light pattern directed towards the reflective interior of the envelope and thereby greatly cut down the efficiency of such light sources by eliminating a portion of radiation that otherwise would be effectively utilized in its operation.

In addition, prior devices have been largely unable to develop a tight or small radius of circular movement of the rotating anode spot necessary for the present anode.

It is the general object of this invention to provide a high-intensity arc-discharge light source which may be 3,378,713 Patented Apr. 16, 1968 operated with high ambient pressures and a high input power while also achieving a high efiiciency.

It is another object of this invention to provide a high-intensity arc-discharge light source having a specially formed anode which provides increased efliciency of operation and minimizes heat transfer limitations.

A further object of this invention is to provide magnetic means within an anode of such arc-discharge light sources.

A still further object is to provide magnetic means located forwardly of such anode of a high intensity are discharge light source to provide magnetic lines of force into the arc discharge.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing an enclosing envelope within which is provided an anode having an aperture axially extended therethrough and a cathode spaced and insulated from the anode. The anode and cathode are operatively positioned with respect to each other and are energizable to sustain an intense arc-discharge therebetween. A magnetic means is provided within the anode which, when actuated, creates a magnetic field with a radial component external of the anode causing lines of force to intersect the discharge-arc and result-in a rotating motion imparted to the are around the axis of the anode on the end of the anode.

For a better understanding of the invention, reference should be had to the accompanying drawings wherein:

FIG. 1 is a vertical longitudinal sectional view of a discharge source and employing an anode constructed in accordance with the present invention;

FIG. 2 is a fragmentary enlarged longitudinal view, shown partly in section, of the anode of the present invention and showing the magnetic field associated therewith;

FIG. 3 is an enlarged vertical sectional view of the anode taken along the line III-J11 in FIG. 2 in the direction of the arrows; and

FIG. 4 is an enlarged diagrammatic view of the tips of the anode and cathode and showing the circular arc path.

With specific reference to the form of the invention illustrated in the drawings, the device 10 as shown in FIG. 1 generally comprises an envelope 12 of predetermined dimensions and configurations. In the embodiment as shown, the main body 14 of the envelope is preferably of stainless steel and preferably is provided with cooling means, not shown, such as continuously circulating water over its exterior surface.

The interior surface of the envelope body portion 14 is formed as a radiation-reflecting ellipse 16 having a first focal point F positioned within the envelope and having a second focal point F positioned exterior of the envelope. A face member 18, also preferably of stainless steel, is afi'ixed to the envelope body portion by means such as screws 20 and carries a thick, radiation-transmitting quartz window 22, positioned with respect to the focal point F such that all radiations generated proximate to the focal point F are directed toward the window 22.

A series of gas inlet apertures 24 are positioned to open into the envelope 12 around the quartz window 22. A discharge-sustaining gas, such as argon, is introduced through an inlet tube 26, into a manifold 28 and is caused to pass through the apertures 24 to produce a vertical path with respect to the axis of the ellipse and directed generally toward the internal focal point F providing an effective gas barrier between the interior of the elliptical reflector 16 and any vaporized electrode material and, in addition, assists in providing stiffness to the formed arc.

The cathode 30 is formed of tungsten and the end portion thereof 32 has the figure of a truncated cone. To help dissipate the heat which is generated when the source operates, a cooling medium such as water is pumped into the water inlet 38, as shown in FIG. 1, and is circulated into the body of the cathode through the inlet tube 40. The heated water is returned through the outlet tube 42. Further details of the device 10 are described in aforementioned Patent 3,280,360.

The anode 34 is shown in greater detail in FIGS. 2 and 3 and is formed of tungsten, copper, or other suitable material having a high thermal conductivity and a high melting point. The anode itself is generally constructed in two sections joined together at a point such as 36. The main body of the anode 34 is generally cylindrical, terminating in a truncated cone, the end section 38 of which is generally flattened and is positioned generally in a perpendicular plane to the cathode.

The generally flattened anode end portion 38 has an area substantially greater than the cross-section area of the arc-discharge 40 (see FIG. 4) adapted to be sustained between the cathode and the anode in order to provide sufficient area for the rotational movement of the arc.

An aperture 42 is provided along the axis of the anode 34 and is extended through the envelope 12. Initially, the cross sectional area of this aperture 42, as provided through the flattened end portion 36, is substantially smallor than the arc-discharge 40 adapted to be sustained between the anode 34 and the cathode 30. In this way, an appreciable amount of the discharge plasma is prevented from entering the aperture 42 and thus avoid melting of the anode.

Cooling means is provided during operation by a cooling tube 44 which introduces water through its interior 46 to the body portion of the anode. A hollow core 48 of a suitable magnetic material, such as soft iron, is affixed to the end of cooling tube 44 such as at 46 so that their respective internal diameters are generally in alignment in order to provide a clear channel for cooling water introduced through the cooling tube 44. The thickness of the hollow core 48 is generally greater than that of the cooling tube 44 and is designed to produce the optimum magnetic characteristics desired.

The cooling water flows through the interior of hollow core 48 and is returned concentrically external 0f the hollow core and the cooling tube 44, as shown generally by the area 50.

The hollow core 48 is adapted to extend substantially into the anode 34 and terminates in an open end 52. A suitable electrical insulating material 54, such as commercial vinyl plastic electric tape, is provided on the external surface of the hollow core 48 to provide electrical insulation of its external surface throughout most of its entire length.

An electrical conductor 56 is wound spirally around the hollow core 48 for a substantial portion of its length. In the preferred embodiment as shown, the electrical conductor is a fiat rectangular copper strip, such configuration having been found most convenient to wind in the desired fashion.

The electrical conductor 56 is electrically insulated from the hollow core 48 by means of the insulating material 54 through most Of the length of the conductor and makes electrical contact with the hollow core 48 at the end of said conductor such as at 58, proximate the open end 52 of said hollow core. The electrical connection 56 may be made by any suitable means and a soldered connection has been found most convenient.

A suitable source of electrical energy, either AC or DC, not shown, is provided, one pole of which is connected to the electrical conductor 56 through the use of a lead wire such as 60 at the end of conductor 56 opposite that end connected to the hollow core 48. Such a connection is shown at 62 and may be made at any convenient point along the conductor 56 which is removed from the spirally wound section. The remaining pole of the electrical source is connected to the cooling tube 44 at any convenient point along its length 64, said connection being made by use of a lead wire 66. In this arrangement, the electrical current is sustained through the electrical conductor 56, the hollow core 48 and the cooling tube 44, all in electrical series connection.

Although it is believed that the foregoing description is sufficient to make the operation apparent, the following review of its operation will be made.

The device 10 is started by applying an energizing potential across the anode 34 and cathode 30 suflicient to create a discharge are 40 between the two as shown in FIG. 4. Discharge-sustaining gas is introduced through the inlet tube 26 and swirls in its vortical pattern. This discharge-sustaining gas coupled with the high pressure within the envelope 12 tends to create a highly intense arc of relatively small cross-sectional area. The radiations thereby generated at the focal point P are reflected toward the quartz window 22 and are concentrated generally at the second focal point P The electrical source is energized, causing a predetermined amount of current to How through the lead wire 60, electrical conductor 56, hollow core 48, cooling tube 44 and lead wire 66.

This fiow of current causes a magnetic field to be set up external of the anode and is assisted by the soft iron core material. The lines of force of the magnetic field are shown generally in FIGS. 2 and 4 and are roughly parallel to the anode axis, with a radial component in the region of the arc-discharge.

The arc 40 as initiated, is at angle to the orientation of of the anode, due generally to the presence of the aperture 42 which is removing discharge-sustaining gas during operation of the device 10.

The arc therefore is formed between the tip of the cathode and some point on a circular locus '68 on the flattened end portion 36 of the cathode 34.

The conducting are 40 contains charged particles, electrons and ions, which are directed through the magnetic field lines established exterior to the anode. The ions, as directed through this magnetic field, have exerted on them a component of force generally perpendicular to their movement, or are movement, at any point in its operation. This component of force sets up a motor action, exerting a force perpendicular to the flow of ions as well as perpendicular to the direction of the field and, as a result, causes the are 40 to move continuously in a circular motion.

The speed of this circular motion is dependent on the value of the arc current and the strength of the magnetic field. As a practical value, excellent results are attained with an electrical conductor of approximately 8 turns operating at amperes. The device was used at these values for many hours of service, with water cooling of the anode, and with no notice of degration or decrease in its effectiveness.

It will be recognized that the objects of the invention have been achieved by providing a high-intensity arcdischarge light source which may be operated at higher power inputs and greater efficiencies. There is provided a novel means internal of the anode of such a device, for continuously rotating an arc struck from the anode, thereby avoiding high heat localities and allowing greater power to be utilized in maintaining the are without the resultant heat transfer limitations.

While a best embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or 0 thereby.

anode, and an internal core portion within said anode coaxial with said aperture;

(c) a cathode positioned within said envelope and operatively spaced and insulated from said anode;

(d) means to maintain a high intensity electric arc between said anode and said cathode; and

(e) an electrical conductor spirally wound about the substantial length of said internal core portion, and adapted to be energized to generate a magnetic field which extends external of said anode and which intersects the high intensity electric are between said anode and said cathode, whereby the resultant magnetic force causes said are to rotate on the end surface of said anode.

2. A plasma jet apparatus comprising:

(a) envelope means of predetermined dimensions and configuration;

(b) discharge-sustaining gas supply means extending into said envelope means;

(c) an elongated anode positioned within said envelope, an aperture extending axially through said anode, and an internal core portion within said anode coaxial with said aperture;

(d) cooling means internal of said anode adapted to pass a cooling liquid continuously within said anode;

(e) a cathode positional within said envelope and operatively spaced and electrically insulated from said anode;

(f) means to generate and maintain a high intensity electric arc between said anode and said cathode; and

(g) an electrical conductor spirally wound about the substantial length of said internal core portion, and adapted to be energized to generate a magnetic field which extends external of said anode and which intersects the high intensity electric are between said anode and said cathode, whereby the resultant magnetic force causes said are to rotate on the end surface of said anode.

3. A plasma-jet apparatus comprising:

(a) envelope means of predetermined dimensions and configuration, said envelope means having a focal point positioned within its interior;

(b) discharge-sustaining gas supply means extending into said envelope adapted to pass a dischargesustaining gas therethrough directed toward said focal point;

(e) a hollow elongated anode positioned within said envelope means, said anode located proximate said focal point and provided with an aperture axially extended therethrough, said aperture adapted to remove a portion of discharge-sustaining gas;

(d) cooling means internal of said anode adapted to pass a cooling liquid continuously within said anode;

(e) a cathode positioned within said envelope and operatively spaced and electrically insulated from said anode, said cathode being located proximate said anode and generally in axial alignment therewith,

(f) cooling means within said cathode;

(g) means to generate and maintain a high intensity electric are between said anode and said cathode; (h) a hollow core positioned with said hollow elongated anode;

(i) an electrical conductor spirally wound about said hollow core and electrically insulated therefrom substantially along the length of said hollow core, said electrical conductor making electrical contact with said hollow core only at a location proximate the end of said core which is proximate the high-intensity are between said anode and said cathode, said electrical conductor adapted to be energized to generate a magnetic field external of said anode which field intersects the flow of ions in said high intensity arc, thereby creating a resultant force on said ions and imparting a rotating motion to said arc on said anode.

4. A plasma-jet apparatus comprising:

(a) envelope means of predetermined dimensions and configuration, a portion of said envelope means being radiation transmitting, another portion of said envelope means being radiation reflecting and in general elliptical shape, said envelope means having a focal point positioned within its interior, and the relative positioning of the radiation-reflecting portion and the radiation-transmitting portion being such that substantially all radiations generated proximate said focal point are ultimately directed toward the radiation-transmitting portion;

(b) discharge-sustaining gas supply means extending into said envelope means and adapted to pass a quantity of discharge-sustaining gas into said envelope means in a generally vortical pattern and directed generally toward said focal point;

(e) a hollow elongated anode positioned within said envelope means proximate said focal point, said anode provided with an aperture axially extended therethrough, the cross-sectional area of said aperture at the end of said anode being substantially less than the cross-sectional area of the arc discharge adapted to be sustained by said anode, said aperture adapted to remove a portion of discharge-sustaining (d) a cooling tube positioned substantially within said anode and adapted to pass water through its interior and into said anode, said water being discharged concentrically external of said cooling tube within said anode;

(e) a cathode positioned within said envelope and operatively spaced and electrically insulated from said anode and in axial alignment therewith;

(f) cooling means adapted to circulate cooling water internal of said cathode;

(g) means to generate and maintain a high intensity electric arc between said cooled anode and said cooled cathode; and

(h) a spirally wound electric conductor internal of said hollow elongated anode along its length and adapted to be energized to generate a magnetic field external of said anode which intersects the high intensity electric are between said anode and said cathode, whereby the resultant magnetic force causes said arc to rotate on said anode in a generally circular pattern.

5. In an electrical plasma-jet apparatus, an anode construction comprising:

(a) an elongated electrode having an aperture extending therethrough, an internal core portion within said electrode coaxial with said aperture;

(b) cooling means internal of said electrode;

(c) an electrical conductor spirally wound about the substantial length of said internal core portion, and adapted to be energized to generate a magnetic field which extends external of said elongated electrode and which intersects the high intensity electric arc between the cathode and said elongated electrode, whereby the resultant magnetic force causes said are to rotate on said end surface of said electrode.

6. In an electrical plasma-jet apparatus, an anode construction comprising:

(a) a hollow elongated electrode capable of passing a large current to maintain a high-intensity electric arc proximate one end thereof;

(b) cooling means internal of said electrode and adapted to pass a cooling liquid continuously within said electrode;

(c) magnetic field generating means positioned Within said electrode, said magnetic field generating means comprising;

(1) a hollow core of magnetic material positioned within said hollow elongated electrode,

(2) an electrical conductor spirally wound about said hollow core along at least a part of its length and electrically insulated therefrom throughout most of the length of said hollow core;

(3) said electrical conductor making electrical contact with said hollow core only at a location at the end of said hollow core which is proximate the electrode end adapted to receive the high-intensity electrical arc, said electrical conductor and said hollow core thereby being in electrical series relationship whereby an electric current may be caused to flow through said conductor and said hollow core and thereby create a magnetic field external of said electrode and proximate the high-intensity arc, said magnetic field causing said high-intensity arc to continuously rotate in a circular pattern on said anode.

7. In an electrical plasma-jet apparatus, an anode construction comprising:

(a) a hollow elongated electrode capable of passing a large current to maintain a high-intensity electric arc proximate on end thereof, said electrode provided with an aperture extending axially therethrough;

(b) a cooling tube extending within said electrode and adapted to pass cooling water through the interior of said tube and allow such water to exhaust concentrically external of said tube;

(c) a hollow soft iron core afiixed to said cooling tube in electrical contact herewith and extending a distance further into said elongated electrode toward the end of said electrode adapted to maintain th high-frequency electric arc; ((1) electrical insulating means substantially covering the exterior surface of said hollow soft iron core; (e) an electrical conductor spirally wound about said hollow core and electrically insulated therefrom throughout most of the length of said hollow core by said electrical insulating means; and (f) said electrical conductor making electrical contact with said hollow core only at the end of said hollow core which is proximate the end of said hollow core which is proximate the electrode end surface that is adapted to maintain the high-intensity electric arc and said electrical conductor, said hollow core and said cooling tube and thereby generate a magnetic field external of said electrode and proximate the end of said electrode adapted to maintain the high-intensity arc whereby said magnetic field creates a component of force to be exerted on said electric arc resulting in motor action t-herebetween and causes said electric arc to rotate in a circular pattern on said anode.

References Cited UNITED STATES PATENTS 1,039,011 9/1912 Beck 313-155 X 2,508,954 5/1950 La Tour, et al. 3l3-156 X 3,048,736 8/ 1962 Emmerich 313-231 X 2,931,889 4/ 1960 Liugafelter 2l9123 FOREIGN PATENTS 933,284 9/1955 Germany.

DAVID J. GALVIN, Primary Examiner. 

